We can login into salesforce without using the salesforce username & Password
Step 1 : Go to Developer Console
Step 2 : Execute this below apex code
String baseUrl = URL.getCurrentRequestUrl().toExternalForm().substringBefore ('/services/');
String sessionID = UserInfo.getOrganizationId()+''+UserInfo.getSessionId().subString(15);
system.debug(baseUrl+'/secur/frontdoor.jsp?sid='+sessionID);
In Debug Log you will get full URL now using URL you can login into your org